1. Field of the Invention
The present invention relates to the production of viscous polybutenes and more particularly relates to a method and apparatus for controlling the molecular weight of the polymeric butene product output from a polybutene reactor.
2. Description of the Prior Art
The manufacture of viscous polybutenes using a Friedel-Crafts catalyst system fed by a mixed butene monomer stream has been known for a long time. Various methods and apparatus using a Friedel-Crafts catalyst system for producing polybutenes are disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 2,320,256 Bailey, et al. 2,469,725 Heinrich 2,657,246 Schneider, et al. 2,673,957 Fontana, et al. 2,957,930 Jackson 3,119,884 Allen, et al. 3,501,551 Heidler, et al. 4,306,105 Abernathy et al. 4,400,493 Abernathy, Jr, et al. 4,420,008 Shu ______________________________________
Heretofore it has been known that normally olefins containing approximately 4 carbons per molecule can be converted to viscous liquid polymers using Freidel-Crafts catalyst or Lewis acid catalyst, a preferred catalyst being aluminum chloride.
The typical olefin feed stock is a refinery stream from a cracking tower containing mixed butenes and butane, commonly referred to as a "B--B stream".
By controlling the parameters of operation of a polybutene reactor system including a polybutene reactor, a range of viscous polymer products can be obtained typically having molecular weights from approximately 900 up to approximately 5000.
The parameters that are controlled are the temperature of the reactor and the catalyst concentration in the reactor.
Although general correlations are known between the final molecular weight of the product output and the various controlled parameters such as temperature and catalyst concentration, it has heretofore been difficult to make adjustments to these parameters without knowing the actual molecular weight of the product as it is produced in order to obtain a desired molecular weight of the product output.
Since conventional laboratory techniques for the determination of molecular weight involve a relatively long procedure, such laboratory determination has been unsuitable for use in a polybutene reactor system for controlling input variables. Thus, it is desirable to provide some means, e.g., a method and/or an apparatus, for effecting immediate changes of controlled variables in response to the molecular weight of product as it is being produced. Such a method by which the molecular weight of the viscous polyolefin (polybutene) product output can be determined as it is being produced is very desirable since the information about the molecular weight of the product output could be used to immediately adjust controlled parameters of the polybutene reactor system.
As will be described in greater detail hereinafter, the method and apparatus of the present invention differ from the previously proposed methods and apparatus by providing a method and apparatus for monitoring certain concentrations of specific olefins in the feed stream and/or the reactor as well as the temperature of the reactor and including an empirically determined model by which the molecular weight of the polybutene product output can be predicted. Based upon a predicted or mathematically calculated molecular weight, a control circuit for the polybutene production system can determine what parameters should be altered or adjusted to produce a polybutene product output having a desired precise molecular weight.